This invention relates in general to control systems for prime movers and in particular to a reference signal circuit whereby bumpless transfer between automatic, manual and memory modes of operation is provided.
Computer automated control is rapidly becoming the preferred mode of operation for prime movers such as steam turbines employed in power generating stations and industrial installations. Despite a growing trend toward automation and the inherent reliability of computers, it is still mandatory to retain a manual control for the prime mover particularly in the event of emergencies and other unique situations. In addition, it is desirable to provide automatic to manual transfer in either a planned or emergency situation without undue disruption of the control system. Likewise, manual to automatic transfer should also be provided in a so-called "bumpless" manner. Finally, it is desirable to provide a temporary last valid signal memory function should the automatic input signal to the control system fail.
U.S. Pat. No. 4,025,762 issued May 24, 1977 to Rossi and Behringer and assigned to the assignee of the present invention shows circuitry for retaining a last valid automatic input signal prior to transfer to a manual mode. "Bumpless" transfer into the manual mode is accomplished by aligning the manual signal input to match the last valid automatic signal. The present invention improves upon the state of the art by providing an automatic tracking circuit which obviates the process of initializing the manual control to the automatic control prior to transfer.
U.S. Pat. No. 4,227,072 issued Oct. 7, 1980 to Fancy and Behringer and assigned to the assignee of the present invention shows a reference signal circuit which provides for either local or remote manual input into a signal reference circuit. The patent teaches the details of manual pushbutton input and priority for a prime mover control. The present invention discloses further bumpless transfer from the automatic mode into the manual mode in either a planned or emergency situation while also allowing bumpless transfer from the manual to automatic mode when deemed appropriate to the operation of the prime mover.
Also provided, is a circuit for automatically testing an overspeed condition in the manual mode and then returning automatically to a high speed stop (HSS) upon cessation of the overspeed test.